FIG. 1 is a simplified schematic diagram illustrating imaging optics used to collimate the light from an optical fiber 104. As is typical, the distal end of the fiber is spaced apart from the surface of lens 102 used for collimation. Not only does this arrangement require precise mechanical locating (and re-locating) to laterally and axially align the fiber relative to the lens, if the fiber is carrying high-power laser light, as might be the case with Raman probes, this results in a high energy density in the air space between the tip of the fiber and the imaging optics. As a result, couplings of this kind must be sealed and/or purged to meet safety or environmental requirements.